PROCESSING SUNSHINE DURATION MEASUREMENTS FOR THE ASSESSMENT OF SOLAR RADIATION IN CLIMATIC REGIONS OF THE CENTRAL AFRICAN REPUBLIC

The objectives of this work carried out in the Central African Republic are to propose new correlations between the components of solar radiation and the sunshine duration on a horizontal surface on the ground, and then to make an evaluation of the solar potential in the cities of Bambari, Birao and Bangui. Polynomial regression models were used and their parameters were estimated by the ordinary least squares method. A statistical evaluation allowed us to compare the performance of the models. The best correlations are then used to estimate the global and diffuse radiation. In the city of Birao, the estimated global radiation is around 6 kWh/m2.j and the diffuse radiation around 2 kWh/m2.j ; in Bambari the global radiation is around 5.4 kWh/m2.j and the diffuse around 2.3 kWh/m2.j ; in Bangui the global radiation is around 5 kWh/m2.j and the diffuse radiation around 2.3 kWh/m2.j. The potential solar in all these regions is very favorable for small and large-scale solar photovoltaic applications.

Numerical Investigation for Performance Enhancement of Photovoltaic Cell by Nanofluid Cooling

The cooling fluid is a key factor in cooling photovoltaic (PV) panels especially in the case of concentrated irradiance. Maintaining the panel at low temperature increases its efficiency. This paper investigates the usage of water-Al2O3 as a nanofluid for achieving the required cooling process. The particle concentrations and sizes are investigated to record their effect on heat transfer and pressure drop in the developing and developed regions. The research was performed using ANSYS CFD software with two different approaches: the single phase with average properties, and the discrete phase with the Eulerian-Lagrangian frame-work. Both approaches are compared to experimental results found in the literature. Both approaches show good agreement with the experimental results, with some advantage for the single-phase model both in processing time and in predicting heat transfer in the concentration range of 1-6% by volume. It was shown that, the heat transfer coefficient is greatly enhanced by increasing the particle concentration or decreasing the particle size. On the other hand, the usage of nanofluid causes a severe increase in the pumping power, especially with the increase in concentration and the reduction in particle size. Thus, a system optimization was suggested in order to raise the overall system efficiency for photovoltaic applications.

Effect of quartz aperture covers on the fluid dynamics and thermal efficiency of falling particle receivers

Falling particle receivers are an emerging technology for use in concentrating solar power systems. In this work, quartz half-shells are investigated for use as full or partial aperture covers to reduce receiver thermal losses. A receiver subdomain and surrounding air are modeled using ANSYS® Fluent®. The model is used to simulate fluid dynamics and heat transfer for the following cases: (1) open aperture, (2), aperture fully covered by quartz half-shells, and (3) aperture partially covered by quartz half-shells. We compare the percentage of total incident solar power lost due to conduction through the receiver walls, advective losses through the aperture, and radiation exiting the aperture. Contrary to expected outcomes, results show that quartz aperture covers can increase radiative losses and result in modest to nonexistent reductions in advective losses. The increased radiative losses are driven by elevated quartz half-shell temperatures and have the potential to be mitigated by active cooling and/or material selection. Quartz half-shell total transmissivity was measured experimentally using a radiometer and the National Solar Thermal Test Facility heliostat field. Average measured total transmissivities are 0.97±0.01 and 0.94±0.02 for concave and convex side toward the heliostat field, respectively. Quartz half-shell aperture covers did not yield expected efficiency gains in numerical results due to increased radiative losses, but efficiency improvement in some numerical results and the performance of quartz half-shells subject to concentrated solar radiation suggest quartz half-shell aperture covers should be investigated further.

Aerodynamic Design and Wind Tunnel Tests of Small-scale Horizontal-axis Wind Turbines for Low Tip Speed Ratio Applications

In recent times, the application of small-scale horizontal axis wind turbines (SHAWTs) has drawn interest in certain areas where the energy demand is minimal. These turbines, operating mostly at low Reynolds number (Re) and low tip speed ratio (λ) applications, can be used as stand-alone systems. The present study aims at the design, development, and testing of a series of SHAWT models. On the basis of aerodynamic characteristics, four SHAWT models viz., M1, M2, M3, and M4 composed of E216, SG6043, NACA63415, and NACA0012 airfoils, respectively have been developed. Initially, the rotors are designed through blade element momentum theory (BEMT), and their power coefficient have been evaluated. Thence, the developed rotors are tested in a low-speed wind tunnel to find their rotational frequency, power and power coefficient at design and off-design conditions. From BEMT analysis, M1 shows a maximum power coefficient (Cpmax) of 0.37 at λ = 2.5. The subsequent wind tunnel tests on M1, M2, M3, and M4 at 9 m/s show the Cpmax values to be 0.34, 0.30, 0.28, and 0.156, respectively. Thus, from the experiments, the M1 rotor is found to be favourable than the other three rotors, and its Cpmax value is found to be about 92% of BEMT prediction. Further, the effect of pitch angle (θp) on Cp of the model rotors is also examined, where M1 is found to produce a satisfactory performance within ±5° from the design pitch angle (θp, design).

IMAGE ANALYSIS OF PARTICLE FLOW IN CENTRIFUGAL SOLAR PARTICLE RECEIVER

Particle solar receivers promise economical and operational advantages compared to the molten salt based solar receivers. In this study, an experiment is designed to observe the particle flow characteristics in the Centrifugal Solar Particle Receiver. A set of experiments for various receiver rotation speeds and particle mass flow rates is conducted, and experimentally obtained raw results are post-processed by means of an Image Processing Routine based on 4BestEstimate algorithm[1]. The axial advance of the particles in one turn, the particle film thickness and the ratio of the stationary zone to the receiver circumference are measured in order to be later used in the validation study of the Discrete Element Method based numerical model.

Center-Oriented Aiming Strategy for Heliostat with Spinning-Elevation Tracking Method

Spinning-Elevation (SE) tracking system produces a decent image on the receiver surface; however, it is subjected to large variations in tracking speed. In this research, a Graphical Ray Tracing (GRT) model for Center-Oriented Spinning-Elevation (COSE) tracking method is developed to evaluate tracking angles. Instead of a target, a heliostat is pointed towards the on-field center point of the tower. Therefore, a spinning-axis of rotation is a line joining a heliostat, and a center of the tower and elevation-axis is perpendicular to it. This aiming strategy has shown a substantial reduction in rotations of spinning-motor. In contrast, the elevation-motor runs at slightly higher rotations than the target-oriented SE method for the same application. Also, COSE tracking method obtains better shape of the reflected image with less aberration on the receiver surface as compared to SE and the traditional Azimuth-Elevation (AE) method.

Experimental and Numerical Investigation of a Semispherical Solar Still, Chamber Stepwise Basin, with and without a PV Powered Electrical Heater

The world's need for drinkable water is increasing with a growing population. The desalination process using solar energy is the cheapest and most straightforward method that can be used to generate pure water from saline water by utilizing energy from the sun's free heat source. A semispherical and chamber stepwise basin solar still with an inclined glass cover, with and without PV powered electrical heaters as another power source can increase the rate of evaporation of saline water, thus increasing the productivity of semispherical solar still. In this investigation, a conventional solar still and semispherical solar still with and without PV-powered electrical heaters were invented and worked in parallel with the experimental setup to make a good comparison between these models. The experimental results show that stepped semispherical with PV-powered electrical heater and without PV-powered electrical heater solar stills enhanced the productivity of freshwater from a conventional solar still by 156.6% and 72.5%, respectively. The theoretically simulated model is obtained using Mathcad software, and is compared with experimental results. Semispherical solar still productivity increases with increased solar intensity and with a PV-powered electrical heater as an additional power source. The theoretical results concluded from the mathematical model are in good agreement with experimental results.

An in-depth Experimental Investigation of the Outdoor Performance of Wafer and Thin Film PV Technologies in a Tropical Climate

The photovoltaics (PV) industry is booming at an impressive rate. Knowledge of the outdoor perfor-mance of different PV technologies under different climatic conditions is becoming increasingly im-portant for all stakeholders. The aim of this research was to perform the outdoor characterisation of three PV technologies in a tropical climate and evaluate their performances with the aid of a set of key performance indicators. An innovative energy autonomous outdoor test facility has been used to measure the weather conditions and the IV curves of mono-Si, poly-Si and CIGS PV modules. Each IV curve was sampled within less than a second, for every 10 minutes, between sunrise and sunset for a whole year, representing a data set of around 28,000 IV curves of 240 points each. The variations of current, voltage and power were thoroughly studied for changes in temperature and irradiance. This paper reports the variations of temperature coefficients of current, voltage and power with the inten-sity of light. While PV module documentation only present the temperature coefficients of the short circuit current and open circuit voltage at Standard Test Conditions, this paper additionally provides highly valuable information to PV system designers on the variation of these coefficients in the field. The research is also the first to report the variations of the fill factor with temperature and irradi-ance. In general, the wafer technologies were found to have a better performance than the thin film technology. Moreover, the open-circuit temperature coefficient was found to improve for higher irra-diances only for the wafer technologies, while that for the thin-film technology experienced a degrada-tion. The temperature coefficient of current for the mono-Si module was found to be positive at low irradiance levels, but negative at higher irradiance levels.

Feasibility Study of long term Dual Tank PV/T Indirect Parallel Solar Assisted Heat Pump systems

A novel dual tank PV/T indirect parallel solar assisted heat pump system (DTPV/T-ISAHP) was investigated in this paper, which filled a gap in the literature. Furthermore, a long-term performance study analysis was performed under Tunisian climate to offset domestic electric and hot water loads. Optimal operations of such a system are achieved based on a simplified mathematical model. Results showed that the average thermal and electric energy efficiency is about 39.65% and 11.38%, respectively. Results revealed that the increase in solar radiation results in an improvement of the system's thermal-based COP efficiency coefficient reaching 4.49 at 893 W/m2. PV/T average electrical energy output is found to 0.68 kWh/m2/day with an annual average of 177.42 kWh/m2, which leads to an annual electricity surplus of about 5.83%. A reversible heat pump operation seemed more advantageous especially in the summer months, reducing yearly electric demand by about 84.57%. An economic analysis is undertaken and a payback period of about 12.7 years is found. The current study provided a framework for assessing such a system's behavior and providing useful flexibility to achieve the best possible system performance.

Thermal and optical behavior of novel phosphate-based inorganic mixtures containing Fe and Na and their application as solar reflective coating

Herein, the synthesis of the novel and inexpensive phosphate mixtures (calcined and non-calcined) of iron (Fe) and sodium (Na) and their application as reflective coating with building envelope materials is reported. The main objective of this work is to determine the effect of hydrated mixtures as a reflective coating. To obtain different hydrated mixtures, samples were synthesized as both calcined and non-calcined mixtures. Various measurement techniques were used to characterize and study the thermal behavior of mixtures. From the thermal behavior of the mixtures, it is noticed that the mixtures can be used as heat-dissipating materials. The average crystallite size was found 40.18 nm and 25.48 nm for the calcined and the non-calcined mixtures, respectively. The calculated band gap for the calcined mixture is 3.71 eV and the non-calcined mixture is 3.73 eV. According to Reddy's equation, the refractive index of the calcined and the non-calcined mixtures is 2.61 and 2.60, respectively. Both the calcined (1A) and the non-calcined (1B) mixtures were fabricated with commercial white paint to develop aesthetic light gray coatings. Both coatings were painted and tested on two building material slabs separately. Then, the highest reflective coating material between these two was painted on a house prototype and tested against commercial gray paint available in the market. An average temperature reduction of 3.8 K was observed in modified gray coating compared to commercial building paint. The reflective coating of the calcined mixture blended with white paint was observed to be better than the non-calcined mixture blended with white paint.